Wigs have been manufactured and used since ancient age with natural hair as the material, but recently such problems as the supply limitation of natural hair material and others caused the manufacture to increase using synthetic fibers as hair material for wigs. In this case, the synthetic fiber to be used is selected with the primary target that it is basically close to natural hair in terms of feeling and physical properties.
The artificial hair materials to be used are synthetic fibers of acrylic, polyester, and polyamide in many cases, but acrylic fibers in general have low melting point and poor heat stability, so that they have such weak points as poor shape preservation after style setting by heat treatment, resulting in distortion of setting, for example, such as curl and the like when contacted to warm water. Polyester fibers excel in strength and heat stability, but have too high bending rigidity, in addition to extremely low moisture absorbency compared with natural hair, resulting in appearance, feeling, or physical properties different from natural hair, for example, in the environment of high humidity, and they give markedly uncomfortable feeling when used for wigs.
Here, the bending rigidity is the physical property correlating to such feeling as tactile and texture of fibers, and is widely recognized in fiber and textile industries as such that capable of numerical expression by KAWABATA method of measurement (See Non-Patent Reference 1.) Also, an apparatus has been developed which can measure the bending rigidity using a single strand of fiber or hair (See Non-Patent Reference 2.) Said bending rigidity is also called bending hardness, and is defined as the reciprocal number of curvature change generated when a unit bending moment is applied to artificial hair. The larger the bending rigidity of artificial hair, the less bendable, the more resistant to bending, that is, the harder and the less bendable is artificial hair. In other words, the smaller the bending rigidity, the more bendable and softer is artificial hair.
Since polyamide fibers can offer appearance and physical properties similar to natural hair in many aspects, they have so far been in practical use as the hair for wigs. Especially, the invention by the present applicant of the method of manufacture that can remove unnatural gloss by surface processing provided excellent wigs (See Patent Reference 1.)
Polyamide fibers include linear saturated aliphatic polyamide in which only methylene chains are connected with amide bond as a main chain, for example, such as nylon 6 and nylon 66, and semi-aromatic polyamide in which phenylene units are included in the main chain, for example, such as nylon 6T of TOYOBO Co., LTD. and MXD6 of MITSUBISHI GAS CHEMICAL COMPANY, INC. Patent Reference 1 discloses surface-processed artificial hair of nylon 6 fiber as the material.
On the other hand, the artificial hair using nylon 6T has the bending rigidity higher than the natural hair, and hence it is difficult to manufacture the hair of the same property as natural hair. Therefore, it might be considered to manufacture the fiber having the bending rigidity close to natural hair by melt-spinning of nylon 6 and nylon 6T. But these two resins have too different melting points, and if melt temperature is determined fitting to nylon 6T of higher melting point, then there is too serious a problem in the manufacturing process that nylon 6 having low melting point and relatively poor heat stability is deteriorated by thermal oxidation during melting. Consequently, nylon 6T, the single filament of its sole body or mixture with other resin, has not so far been in practical use as an artificial hair material.
The fiber of sheath/core structure is known as the method to utilize both properties of two kinds of resins. Said fiber comprises as one strand of fiber a core fiber and a sheath fiber surrounding it, and can be a generic fiber, or artificial hair material for wigs, by utilizing respective properties of different two kinds of resins. For example, Patent Reference 2 discloses the fiber of sheath/core structure made of vinylidene chloride, polypropylene, and others, and Patent Reference 3 discloses a polyamide, but modified fiber by blending protein bridged gel into the core part.
Further, since using an ordinary synthetic fiber having transparency as artificial hair causes unnatural gloss, various attempts have been tried to suppress it by making uneven surface to cause opacity, thereby to give the appearance and feeling close to natural hair. The above-mentioned Patent Reference 1 discloses the method of making uneven surface by causing spherulite to be generated and grow, and Patent Reference 4 by treating the fiber surface with chemical reagents. In addition, the method of blast-treating of the artificial hair surface with fine powders such as sand, ice, and dry ice is also known.
Artificial hair to be used for wigs is required primarily to have feeling (appearance, tactile and texture) and physical properties close to natural hair, and in addition, ideally speaking, the physical properties superior to natural hair. As mentioned above, various synthetic fiber materials have their own merits and weak points, respectively, and among them, specific polyamide fibers, especially nylon 6 and nylon 66, are in practical use because of their superior properties, but even they can not be hair-dressed using a hair drier as natural hair.
Patent References 5 and 6 disclose thermoplastic resins capable of deforming their shapes by temperature or external stress, and a string-shaped false hair using said resins which can be used for the hair of dolls.
[Patent Reference 1] Japanese Patent Laid Open Application No. JP S64-6114 A (1989)
[Patent Reference 2] Japanese Patent Laid Open Application No. JP 2002-129432 A (2002)
[Patent Reference 3] Japanese Patent Laid Open Application No. JP 2005-9049 A (2005)
[Patent Reference 4] Japanese Patent Laid Open Application No. JP 2002-161423 A (2002)
[Patent Reference 5] Japanese Patent Laid Open Application No. JP H10-127950 A (1998)
[Patent Reference 6] Japanese Patent Laid Open Application No. JP 2006-28700 A (2006)
[Non-Patent Reference 1] Sen'ikikai Gakkaishi (Journal of Textile Machine Society, Textile Engineering), Sueo KAWABATA, 26, 10, pp. 721-728, 1973
[Non-Patent Reference 2] KATOTECH LTD., Handling Manual of KES-SH Single Hair Bending Tester